It is known that switching into the vehicle's electrical system an electrical consumer having high electrical power results in a high load on the generator. Since switching on the electrical consumer leads to a voltage dip in the vehicle's electrical system, a voltage controller assigned to the generator tries to increase the power supplied by the generator by increasing the exciting current. However, this results in the braking torque caused by the generator being increased in such a way that, especially in response to a low rotary speed of the internal combustion engine, an interfering sudden drop of the rotary speed may occur. In order to minimize such a sudden drop in the rotary speed, measures are provided in systems that have a so-called load-response device which prevents the generator from being loaded too greatly. It is thereby also prevented that a sudden drop in rotary speed occurs in the combustion engine. However, since the required electrical power can no longer be supplied, an undesired voltage dip can now occur.
Such a rotary speed change can be countered, at least in certain operating states, in that a sufficient excess torque is supplied. However, this leads to increased usage, in a disadvantageous manner. As an alternative, the generator adjustment can be specifically slowed down. However, this may lead disadvantageously to an increase in the fluctuations of the voltage of the vehicle's electrical system. Such fluctuations are undesired, however, since they disadvantageously influence the service life of the battery, and are able to damage component parts that are sensitive to voltage. As an alternative, an additional consumer could be switched on in a specified manner via a ramp function. However, this requires a greater switching technology expenditure, and therefore leads to higher product costs. In all the alternatives mentioned, an optimum adaptation to the actually available excess torque is not readily possible.
A method is described in published German patent document DE 39 31 897 for voltage control for generators in motor vehicles, in which, in a first time interval, the generator output voltage is set to a maximum value, so that reliable loading of the vehicle's battery takes place independently of the environmental temperature. In a second time interval, the generator output voltage is regulated usually as a function of the battery temperature, according to a known method. In this context, the establishment of the first time interval takes place as a function of the loading state of the battery.